This invention relates to a hydraulic device having fluid pockets formed by a gerotor gear set. It relates particularly to a commutation system for directing flow to and from the fluid pockets.
Hydraulic devices with fluid pockets formed by gerotor gear sets are known. Typically, gerotor gear sets include a stator having internal teeth and a rotor having external teeth. The number of teeth on the rotor is one less than the number of teeth on the stator. The rotor is eccentrically disposed within the stator and rotates and orbits relative to the stator. The rotor is supported and guided in its rotating and orbiting motion by the teeth of the stator. The teeth of the rotor and stator define the fluid pockets, which expand and contract during the rotary and orbital movement of the rotor.
Various valve constructions have been developed for directing fluid into and out of the expanding and contracting fluid pockets. In one known type of valve construction, shown in U.S. Pat. No. RE. 25,291, a rotatable valve member is spaced from the gear set and connected with the rotor so as to be rotated at the speed of rotation of the rotor. In another known type of valve construction, shown in U.S. Pat. No. 3,288,034, a rotatable valve member is spaced from the gear set and connected with the rotor so as to be rotated at the speed of orbital movement of the rotor. The foregoing valve constructions involve separate valve members and drive connections between the valve members and the gerotor gearset.
Some known types of valve constructions eliminate the use of separate valve elements spaced from the gear set and/or the drive connection between the gear set and the valve elements. For example, in U.S. Pat. No. 3,598,509, a valve plate is coupled to the rotor to rotate and orbit therewith. The valve plate has a circular array of openings with alternate openings connected to high and low pressure, respectively. The valve plate is adjacent one side of the gear set, and the circular array of openings cooperates with the teeth of the stator to valve flow into and out of the expanding and contracting fluid pockets.
In U.S. Pat. No. 211,769, the rotor itself forms the valve for controlling flow into and out of the fluid pockets. The rotor cooperates with a series of dog-leg shaped passages formed in housing members on each side of the rotor. Those passages have radially inward ends disposed along a circle and radially outward ends communicating with the pockets. Each face of the rotor has a pair of concentric pressure areas communicated with the high and low pressures. As the rotor rotates and orbits, the movement of the concentric pressure areas relative to the inward ends of the dog-leg shaped passages valves flow. The arrangement is such that flow is directed into the pockets from one side of the gear set and out of the pockets from the other side of the gear set.
A device with valve structure similar to U.S. Pat. No. 211,769 is shown in German Offenlegungsschrift (OS) No. 2,921,311. In OS No. 2,921,311 one side of the rotor has concentric pressure areas communicated with the high and low pressures and an adjacent valve plate has dog-leg shaped passages therein. Flow is valved at the interface of the rotor and the valve plate, and directed to and from the pockets through the dog-leg shaped passages in the valve plate.
Yet another type of valve structure involving the rotor is disclosed in U.S. Pat. No. 3,825,376. In the device shown in U.S. Pat. No. 3,825,376, high and low pressures are communicated with respective ones of pairs of openings in a manifold plate adjacent to the gear set. The rotor includes a series of triangular shaped openings which widen toward the outer periphery of the rotor and which number one less than the teeth of the rotor. The triangular openings are designed so that in certain positions of the rotor they establish a short circuit between adjacent pockets. The patent describes various positions of the rotor during one orbit, and the described positions show a variation in the number of fluid pockets which are in communication with one port or the other. For example, the patent describes a position in which two pockets are communicated to opposite ports, whereas the three remaining pockets are blocked from the ports. It describes another position in which one pocket is connected to the high pressure port, two pockets are connected to the low pressure port, and the remaining two pockets are interconnected by one of the triangular openings in the rotor. The displacement of such a device for a given size gearset is limited by the fact that in various positions of the rotor two of the five pockets are connected with each other, rather than being connected with one of the ports.